Integrating clinical data from cross-sectional and longitudinal studies

Clinical trials are typically conducted over a population in order to illuminate certain characteristics of a health issue or disease process. These cross-sectional studies provide a snapshot of these disease processes over a large population but do not allow us to model the temporal nature of disease. Longitudinal studies on the other hand, are used to explore how these processes develop over time but can be expensive and time-consuming, and only cover a relatively small window within the disease process. This paper explores a technique for integrating cross-sectional and longitudinal studies to build models of disease progression

Consumer Risk Reactions to Food Product-Harm Crises Over Time: Evidence From Cross-Cultural Field Studies

Consumer/Household Economics, Risk and Uncertainty,

Analysing motivation to do medicine cross-culturally : the international motivation to do medicine scale

Vaglum, Wiers-Jensen & Ekeberg (1999) developed an instrument to assess motivation to study medicine. This instrument has been applied in different countries but it has not been studied cross-culturally. Our aims were to develop a Motivation to do Medicine Scale for use in international studies and to compare motivations of UK and Spanish medical students (UK: n= 375; Spain: n= 149). A cross-sectional and cross-cultural study was conducted. The Vaglum et al. (1999) Motivation to do Medicine Scale (MMS) was used. The original MMS factor structure was not supported by the Confirmatory Factor Analysis. Exploratory Factor Analyses within each country identified four factors: 'People', 'Status', 'Natural Science' and 'Research'. Students scored higher on the 'People' and 'Natural Science' than on the other factors. The UK sample scored higher than the Spanish sample on the 'Research' factor and there were greater difference between genders in Spain for both 'People' and 'Research' factors. The scale is suitable for use in cross-cultural studies of medical students' motivation. It can be used to investigate differences between countries and may be used to examine changes in motivation over time or over medical disciplines

Ferromagnetic to spin glass cross over in (La,Tb)_{2/3}Ca_{1/3}MnO_{3}

In the series La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3}, it is known that the compositions are ferromagnetic for smaller values of x and show spin glass characteristics at larger values of x. Our studies on the magnetic properties of various compositions in the La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3} series show that the cross over from ferromagnetic to spin glass region takes place above x ~ 1/8. Also, a low temperature anomaly at 30 K, observed in the ac susceptibility curves, disappears for compositions above this critical value of x. A mixed phase region coexists in the narrow compositional range 0.1 <= x <= 0.125, indicating that the ferromagnetic to spin glass cross over is not abrupt.Comment: 5 pages, 5 figure

Secondary cytotoxicity of (crosslinked) dermal sheep collagen during repeated exposure to human fibroblasts

We investigated commercially available dermal sheep collagen either cross-linked with hexamethylenediisocyanate, or cross-linked with glutaraldehyde. In previous in vitro studies we could discriminate primary, i.e. extractable, and secondary cytotoxicity, due to cell-biomaterial interactions, i.e. enzymatic actions. To develop dermal sheep collagen for clinical applications, we focused in this study on the release, e.g. elimination, of secondary cytotoxicity over time. We used the universal 7 d methylcellulose cell culture with human skin fibroblasts as a test system. Hexamethylenediisocyanate-cross-linked dermal sheep collagen and glutaraldehyde-cross-linked dermal sheep collagen were tested, with intervals of 6 d, over a culture period of 42 d. With hexamethylenediisocyanate-cross-linked dermal sheep collagen, cytotoxicity, i.e. cell growth inhibition and deviant cell morphology, was eliminated after 18 d of exposure. When testing glutaraldehyde-cross-linked dermal sheep collagen, the bulk of cytotoxic products was released after 6 d, but a continuous low secondary cytotoxicity was measured up to 42 d. As a control, non-cross-linked dermal-sheep collagen was tested over a period of 36 d, but no secondary cytotoxic effects were observed. The differences in release of secondary cytotoxicity between hexamethylenediisocyanate-cross-linked dermal sheep collagen, glutaraldehyde-cross-linked dermal sheep collagen and non-cross-linked dermal sheep collagen are explained from differences in cross-linking agents and cross-links obtained. We hypothesize that secondary cytotoxicity results from enzymatic release of pendant molecules from hexamethylene-diisocyanate-cross-linked dermal sheep collagen, e.g. formed after reaction of hydrolysis products of hexamethylenediisocyanate with dermal sheep collagen. Glutaraldehyde-cross-linked dermal sheep collagen contains residual cross-linking agents, which induce the bulk cytotoxicity. Apart from being sensitive to enzymatic degradation, glutaraldehyde-cross-linked dermal sheep collagen was also found to be sensitive to aqueous hydrolysis. Hydrolysis of cross-links may release cytotoxic products and introduce new pendant molecules within glutaraldehyde-cross-linked dermal sheep collagen, which in turn induce cytotoxicity after enzymatic attack

Using Fractionalization Indexes: deriving methodological principles for growth studies from time series evidence

Recent cross country growth studies have found that ethnolinguistic fractionalization is an important explanatory variable of long-run growth performance. This paper highlights some limitations of cross country studies by focusing on the time series evidence for South Africa. In presenting variation over time in a number of social, political and economic dimensions, this paper adds longitudinal evidence on a range of dimensions that have been linked to long run economic development. Given South Africa’s history of ethnic and racial politics, it constitutes a useful case study to explore the dynamics of the possible effects of ethnolinguistic fractionalization on growth. We introduce three new sets of fractionalization indicators for South Africa and one set of political indicators. The results of this study provide important nuance to the existing body of evidence, for the use of fractionalization indices in growth studies.

Unit root and cointegration tests for cross-sectionally correlated panels - Estimating regional production functions

There is a plethora of studies of regional production functions using stationary panel data. Only some recent works consider non-stationary panel data. All of them assume the hypothesis of cross-section independence. Here, we claim that the independence assumption is too strong when regional data are used. In this paper, the cross-section independence assumption is released and cross-sectional dependence is assumed. First, unit roots and cointegration properties of the panel dataset are properly investigated by using newly developed tests for cross-sectionally dependent panels. Second, dynamic OLS (DOLS) and recent regression models for cross-sectionally correlated panels are used to estimate the cointegrated relationship between value added, physical and human capital, for Italian regions over the period 1970-1998.

The Other Side of the Moon: The Data Problem in Analyzing Growth Determinants

Replication of two recent studies of growth determinants shows that results are sensitive to the choice of data from which growth rates are calculated, especially with respect to whether economic convergence has occurred. Previous warnings against using data that has been adjusted to increase cross-country comparability to study within-country patterns over time (growth rates) have been largely ignored at the cost of possibly contaminating the conclusions.http://deepblue.lib.umich.edu/bitstream/2027.42/40068/3/wp682.pd